Nitrogen is most commonly prepared by the fractional distillation of liquid air or by pressure swing adsorption (PSA) from atmospheric air. Although nitrogen is widely available for use as an inerting gas and as a component in various syntheses reactions among other widely diversified uses, it is still relatively expensive, and cheaper nitrogen sources would be highly beneficial for use in ammonia synthesis and other industrial applications.
In the recovery of nitrogen from atmospheric air by selective adsorption in a pressure swing system, the feed air needs to be compressed and/or a vacuum pump employed for reduction of bed pressure. Nitrogen recovery by PSA is rather low (.about.40-50%) and the mechanical power required constitutes a substantial part of the nitrogen production cost. In the cryogenic air fractionation process, likewise, the feed air needs to be compressed (to about 100 psi) and cooled prior to distillation.
In the synthesis of ammonia by the combination of nitrogen and hydrogen over a catalyst, the hydrogen is commonly produced by steam reforming of methane (SMR), natural gas or other low molecular weight hydrocarbons. The nitrogen can be supplied from a cryogenic air separation plant. However, it is now more common to employ in combination with the primary steam reforming furnace a secondary reformer in which air is injected in an amount to provide the proper H.sub.2 /N.sub.2 ratio.